The present invention relates to an optical apparatus such as a digital still camera, a digital video camera and an interchangeable lens, and particularly to autofocusing (AF) control in the optical apparatus.
Optical apparatuses using a solid-state image-pickup element often employ a so-called contrast AF (TV-AF) in which a focus lens (or a compensator) is moved by using contrast information generated from video signals to obtain an in-focus state.
In addition, such optical apparatuses often employ a zoom optical system of an inner-focus type in which the focus lens (or the compensator) is driven when a variator that is a magnification-varying lens is moved while maintaining a certain optical positional relationship between the focus lens and the variator. Japanese Patent Laid-Open Nos. 4-134307 and 4-134308 disclose such an inner-focus type zoom optical apparatus.
In the contrast AF, changes of the contrast value (value relating to the contrast information) are detected by causing the focus lens to minutely wobble (minutely move to and fro) to determine the direction of an in-focus position in which the contrast value increases, and then the focus lens is moved in the determined direction.
Further, when the contrast value increases and decreases near the maximum level in response to the minute wobbling (minute to-and-fro motion), the position near the center of the wobbling is determined as the in-focus position.
When a back focus of an image-pickup optical system is shortened to reduce the size of the image-pickup optical system in response to a recent demand of miniaturization of the optical apparatus, it is difficult to keep an exit pupil of the image-pickup optical system sufficiently far from an image plane, so that the image-pickup optical system tends to become a non-telecentric optical system.
The minute wobbling in such an image-pickup optical system varies an image magnification, which causes a user to feel anomalous.
Japanese Patent Laid-Open No. 6-205267 discloses an optical apparatus in which the variator is wobbled in association with the wobbling of the compensator to reduce user's discomfort caused by variation of the image magnification.
However, the optical system disclosed in Japanese Patent Laid-Open No. 6-205267 which is a rear-focus type is a near-telecentric optical system, so that the variation of the image magnification caused by the motion of the focus lens (or the compensator) is small. Therefore, twitching of the image is almost unnoticeable even without causing the variator to wobble with the wobbling of the focus lens.
In contrast, in a zoom lens that is a non-telecentric optical system (that is, a zoom lens whose exit pupil position is varied with zooming), the wobbling of the focus lens (or the compensator) causes the image magnification to significantly vary, which may give discomfort to the user.